The human immunodeficiency virus (HIV) and herpes simplex virus (HSV) cause significant morbidity and mortality. While both viruses can be transmitted sexually, people with genital herpes are more prone to HIV. Condoms offer excellent protection, but the effect has been limited due to poor compliance. Alternative prophylaxis, such as microbicides, for use by women are desirable. HIV is an RNA virus, while HSV is a DNA virus, but they both have an envelope with high mannose. Coincidentally, certain lactobacilli naturally capture mannose as a preferred nutrient by a specific binding protein-dependent sugar uptake system. Its sugar-binding protein (lectin) binds mannose. By screening nearly 1,000 oral and vaginal strains for such lectin, we have selected two strains from oral and five from vaginal lactobacilli that can capture and metabolize envelope mannose of HIV/HSV. Therefore, we propose to develop a probiotic microbicide against both HIV and HSV based on Lactobacillus mannose-binding lectin (LMBL). We hypothesize that LMBL+ lactobacilli can block both HIV and HSV infections by mannose-specific binding. This project is to perform preclinical studies. We will pursue five specific aims: (1) phenotypic and genotypic analyses of candidate LMBL+ lactobacilli;(2) document blockage of LMBL+ lactobacilli against HSV-2 and HIV-1 in vitro;(3) test anti-HSV-2 efficacy of LMBL+ lactobacilli in vivo in a mouse herpes model;(4) assess safety of LMBL+ lactobacilli in vivo in rabbits and rats;and (5) optimize formulation, packaging, and shelf life of the probiotic microbicide. Upon completion of this study, we will achieve preclinical data and be ready for clinical trials. Putative advantages of this method include safety, persistent protection and cost-efficiency. Superior to all other, microbicides, the new method can be compliance-independent. It can protect women unobtrusively and inconspicuously. Our long-term goal is to develop a bio-prophylaxis that can serve as an alternative or supplement to vaccines or physical barriers to protect women against sexual transmission of HIV and HSV. We propose to develop a novel method to fight AIDS and herpes viruses with their natural enemies. We have isolated a group of friendly lactobacilli, which can capture viruses for their sugar, thereby killing the virus, much like cats catching mice. Successful development of this method will likely curb the global HIV/HSV pandemic and ultimately save many lives.